I have XP, and NVIDIA is what I have, it is totally awesome! Although, I don’t know if you can just purchase it alone, my computer is custom built, and my computer guy decked it out. But I would suggest NVIDIA to anyone that could get it.

Well, it’s not THAT important.
Nowadays, all manufacturers make XP compatible soundcards.

If you wanna have a slightly better one, choose Creative or Terratec.

What are the uses you want ?
– Game engine acceleration (EAX…) ?
– Studio recording ? (with mics ?)
– Home Cinema playback ?
– Does it have to be multichannel or/and support Dolby D or DTS ?
– Does it have to support hi-quality audio, like 24/96 ?
– Does it have to support SoundFont (cheap sampling) ?
– Does it have to feature hi-perf drivers like ASIO ?
…

You should buy the Creative Sound Blaster Audigy 2 ZS.
It’s not very expensive but a high-quality soundcard,
you could even use 7.1 surround speakes with this thing.
Plus it supports EAX up to version 3.0.